How Do I Fix a Small Leak on the Toilet Water Supply Valve?

Vertical Plumbing
Jul 28
2 min read

Updated: Nov 12

Noticed a small puddle of water behind your toilet? That small drip from the water supply valve may not seem like a significant issue, but if left unattended, it can lead to water damage, mold growth, or even a spike in your water bill.

In this blog, we’ll walk you through the common causes of a leaky toilet water supply valve, how to fix it yourself, and when it’s time to call in a pro.

What Is the Toilet Water Supply Valve?

The toilet water supply valve, also called the shut-off valve, is usually located on the wall behind the toilet. Its job is to control the flow of water to your toilet tank. If it starts leaking, it can cause water to drip onto the floor or the valve itself.

Common Causes of a Leaky Supply Valve

Here are a few reasons your toilet shut-off valve might be leaking:

Loose packing nut
Worn-out washers or seals
Corroded or cracked valve
Loose connection between the valve and supply line

Most small leaks can be fixed quickly, especially if they’re coming from the nut or fittings.

How to Fix a Small Leak on the Toilet Water Supply Valve

Before working on your plumbing, always turn off the main water supply to your home if you're unsure about shutting off just the toilet valve.

Step-by-Step Fix:

1. Tighten the Packing Nut

Use an adjustable wrench to gently tighten the nut behind the valve handle.
Don’t over-tighten, just enough to stop the leak.

2. Replace the Washer or Valve

If the leak continues, the washer inside the valve might be worn out.
Turn off the main water supply.
Remove the valve by unscrewing it from the pipe.
Take it to a hardware store for a matching replacement or washer kit.
Install the new valve or washer and reconnect.

3. Replace the Flexible Supply Line

Sometimes, the leak comes from the connection between the valve and the toilet tank.
If the flexible hose looks worn or cracked, replace it with a new one (they're cheap and easy to install).

When to Call a Professional Plumber in Phoenix

If:

The leak continues after tightening or replacing parts
The valve is corroded or broken
You're uncomfortable turning off the main water supply

Prevent Future Leaks

Inspect plumbing valves annually
Don’t force the valve open or shut, it can damage the parts
Upgrade old valves to newer quarter-turn shutoffs for easier maintenance

A small leak on your toilet’s water supply valve might seem harmless, but it can become a bigger issue fast. With a few simple tools, many leaks can be fixed in minutes. But if you’re unsure or want it done right the first time, don’t hesitate to call a professional.